The present invention relates to a method of and a circuit arrangement for metering or proportioning of ink in a printing machine provided with ink fountain and an ink doctor roller driven by a separate motor.
The metering or dosing of printing ink according to different printing applications by means of an ink fountain provided with an ink blade adjustable by means of zone screws and being in contact with an adjustable ink doctor roller is known since long time. To meet the general requirement for continuously increasing the printing efficiency, a large number of new solutions has been recently devised. However, such known solutions are frequently very complicated in construction.
From the DD-Pat. No. 212 475 a solution is known in which an ink film is metered toward the ink doctor by adjusting zone screws acting on the ink blade. The ink film is periodically withdrawn from the ink doctor by an ink lifter and transferred to the first ink distributing cylinder. The ink lifter is swung by means of a cam roller control in such a manner that every 21/2 rotations of the printing plate cylinder it engages the ink doctor and the first ink distributing cylinder. By means of an electrical control activated by a selector switch it is possible to change the swinging frequency of the ink lifter such that it is brought into engagement with the ink doctor once after each fifth or tenth rotation of the printing plate cylinder.
This known device provides satisfactory ink metering for most applications. Its disadvantage however is the fact that the engagement or contact time of the ink lifter is not adjustable and consequently the ink metering cannot be set with sufficient sensitivity.
In an ink metering device according to DE-AS No. 1 761 394 the ink doctor is driven by the printing machine at a constant rotary speed ratio and the ink is transferred by an ink lifter to the first ink distributing cylinder. The times of engagement of the ink lifter roller with the ink doctor and the first distributing cylinder are adjustable by means of two timing devices which cooperate with a changeover device. The latter device consists of a large number of component parts and is very complex in construction and consequently expensive in manufacture. An accurate reproduction of a preceding setting is not possible on this known device.
A device for ink metering has been also proposed in which the ink is taken off by a milling roller rotating at the speed of the printing machine and being arranged at a minute distance from a shiftable ink doctor roller. An ink lifter roller transfers the ink from the milling roller onto the first ink distributing cylinder. By means of this known device an adequate ink metering can be achieved. Its disadvantage however is the necessity of a large number of components and consequently high manufacturing costs.